Method and apparatus for monitoring deviation of a limb

ABSTRACT

Apparatus is disclosed for monitoring, measuring and/or estimating deviation of a body part of a vertebral mammal. The apparatus includes at least one sensor for measuring rotation of the body part relative to a first frame of reference and for providing data indicative of the rotation. The apparatus also includes a memory device adapted for storing the data and a processor adapted for processing the data to evaluate a deviation of the body part that correlates to the data. The processor may be configured to execute an algorithm for evaluating deviation of the body part. A method of monitoring, measuring and/or estimating deviation of a body part of a vertebral mammal is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The current application is a national-phase entry of Patent CooperationTreaty application no. PCT/AU2013/001295, which has an internationalfiling date of Nov. 8, 2013, and which claims the priority of Australianpatent application no. 2012904946, filed on Nov. 9, 2012. Thespecifications, claims, and figures of both the PCT and Australianapplications are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for monitoring,measuring, estimating and/or providing feedback on deviation of a bodypart of a vertebral mammal such as medio-lateral deviation, also knownas a change in lower extremity angular alignment. Medio-lateraldeviation may manifest during activities and/or movements such assquatting, hopping and/or running.

BACKGROUND OF THE INVENTION

Knee injuries are common and are painful events for recreational andelite sportspersons. A well-documented risk factor for knee injuries isthe degree of change in angular alignment occurring at the knee jointduring a dynamic activity. The change in angular alignment is commonlyreferred to as valgus or varus depending on whether the knee anglesinward (valgus) or outwards (varus). In anatomical terms, alignment ofthe tibial tubercle with the pelvis is also referred to as Q-angle. Thechange in angular alignment of the knee describes the knee movingmedially whilst the foot is fixed to the ground (valgus) or the kneemoving laterally whilst the foot is fixed to the ground (varus),increasing the angle between the femur and the tibia. When movementcausing change in angular alignment of the knee occurs, it may be incombination with flexion of the knee known as tibio-femoral flexion,internal rotation of the femur, pronation of the foot and/or relativeflexion of the hip joint.

Alignment of the knee, hip and ankle as a person squats, jumps, hops,walks or runs has been a regular test or assessment carried out bytherapists when assessing an athlete or sportsperson. The therapist maysubjectively (visually) rate whether the athlete/sportsperson performedthe test well or poorly using a rating system such as 1 (good), 2(average) or 3 (poor).

Although the rating system may provide a subjective impression of valgusor varus movement when squatting or landing from a hop/jump, the test iscurrently not measured objectively and instead is subjectively assessedbased on visual observations. Video techniques may be used to visualisealignment of the femur with the tibia, while software packages may allowa user to align traces on a screen with angular motion of differentlimbs of the body to estimate the valgus/varus angle. Optical trackingmarkers may also be used with high frame rate cameras to capture thistype of movement in a laboratory setting. However, these procedures aretime consuming to post analyse, often have visual occlusions due to limbmovement, do not provide real time data and typically need to becaptured in a controlled environment with access to specialist equipmentand staff.

The method and apparatus of the present invention may at least alleviatethe disadvantages of the prior art. The present invention may alsoprovide real time feedback, while not requiring video analysis, to allowan athlete/player to adjust their movement patterns in real time, basedon the real time feedback.

A reference herein to a patent document or other matter which is givenas prior art is not to be taken as an admission that that document ormatter was known or that the information it contains was part of thecommon general knowledge in Australia or elsewhere as at the prioritydate of any of the disclosure or claims herein. Such discussion of priorart in this specification is included to explain the context of thepresent invention in terms of the inventor's knowledge and experience.

Throughout the description and claims of this specification the words“comprise” or “include” and variations of those words, such as“comprises”, “includes” and “comprising” or “including, are not intendedto exclude other additives, components, integers or steps.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is providedapparatus for monitoring, measuring, and/or estimating deviation of abody part of a vertebral mammal, said apparatus including:

at least one sensor for measuring rotation of said body part relative toa frame of reference and for providing data indicative of said rotation;

a memory device adapted for storing said data; and

a processor adapted for processing said data to evaluate a deviation ofsaid body part that correlates to said data.

The processor may be configured to execute an algorithm for evaluatingdeviation of the body part. The algorithm may be adapted to transformdata from the first frame of reference relative to a second frame ofreference in which the body part performs a movement.

The algorithm may be adapted to integrate the data over a period of timeto provide an angular displacement (θ). The algorithm may be adapted toevaluate a component (θ_(Z)) of the angular displacement representingangular displacement such as valgus or varus angle. The algorithm may beadapted to project the lateral flexion component (θ_(Z)) onto a frontalplane.

The algorithm may be adapted to evaluate a twist component (θ_(X)) ofthe angular displacement representing twist angle. The algorithm may beadapted to compensate the twist component (θ_(X)) by adding an angularoffset (θ_(x0)) to the twist component (θ_(X)). The angular offset(θ_(x0)) caused by components θ_(Y) and θ_(Z) of the angulardisplacement may be determined by θ_(x0)=atan(sin(θ_(Z))/tan(θ_(Y))).

The at least one sensor may include a gyroscope. The at least one sensormay be adapted for measuring rotation around one or more orthogonalaxes. The at least one sensor may further include means for measuringacceleration of the body part relative to an inertial frame of referenceand for providing data indicative of the acceleration. The accelerationmeans may be adapted for measuring acceleration along one or moreorthogonal axes.

The body part of the mammal may include legs and the apparatus may beadapted to monitor rotation components associated with the legs.Respective sensors may be applied to legs of the mammal. The or eachsensor may include an analog to digital (A to D) converter forconverting analog data to a digital domain. The A to D converter may beconfigured to convert an analog output from the or each sensor to thedata prior to storing the data. Capturing angular deviation duringdynamic lower extremity movements may require a sampling frequency thatis at least sufficient and commensurate with frequency of themovement(s).

According to a further aspect of the present invention there is provideda method of monitoring, measuring, and/or estimating deviation of a bodypart of a vertebral mammal, said method including:

using at least one sensor to measure rotation of said body part relativeto a frame of reference and for providing data indicative of saidrotation;

storing said data in a memory device; and

processing said data by a processor to evaluate a deviation of said bodypart that correlates to said data.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one form of apparatus according to the present invention;

FIG. 2 shows a cross-sectional view in the transversal plane of the leftleg and sensor placed on the tibia;

FIG. 3 shows a projection of the θ_(Z) plane onto the frontal plane withtwist update;

FIG. 4 shows test results for a first subject with little or nomedio-lateral deviation;

FIG. 5 shows test results for a second subject with Varus deviation; and

FIG. 6 shows test results for a third subject with Valgus deviation.

DESCRIPTION OF A PREFERRED EMBODIMENT

The present invention is particularly suitable for monitoring andascertaining medio/lateral deviation of the knee of a human subject at agiven point in time and is described herein in this context.Nevertheless, it is to be understood that the present invention is notthereby limited to such applications.

The present invention may monitor medio-lateral deviation of the knee ina variety of environments including indoor and/or outdoor environmentsand for diverse purposes including but not limited to applications suchas monitoring and measuring medio/lateral deviation of the kneeexperienced by athletes in order to identify poor control, preventinjuries, identify lack of muscular control and/or inflexibility, guideadoption of optimal technique, confirm completion of recovery (forinjured athletes) and/or improve overall performance.

The apparatus of the present invention may be placed on the medial partof the shank of a leg to enable monitoring of medio-lateral deviation,also known as valgus/varus of the knee, during squatting, jumping,hopping, walking and/or running. The apparatus may include rotationsensors such as gyroscopes and optionally one or more inertial sensorssuch as accelerometers and/or magnetometers to ascertain medio-lateraldeviation. The apparatus may include a digital processing engineconfigured to execute one or more algorithms. The algorithm(s) may takeaccount of variables such as angle of the tibia with respect to thetransverse plane and/or twisting of the leg during an activity.

Referring to FIG. 1, one form of apparatus according to the presentinvention includes sensors 10, 11 placed along or in-line with tibialaxes of the left and right legs of a human subject 12. Sensors 10, 11are placed on the legs of subject 12 such that the frames of referenceof sensors 10, 11 are defined by axes x,y,z with axes x,z being in theplane of FIG. 1 (front view) and axes x,y being in the plane of FIG. 1(side view). Measurement of Valgus or Varus is defined as rotationaround the y axis.

Each sensor 10, 11 may include a rotation sensor such as a 1D, 2D or 3Dgyroscope to measure angular velocity and optionally a 1D, 2D or 3Daccelerometer to measure acceleration and/or a magnetic sensor such as amagnetometer to measure magnetic field. The positive axes on both legsmay point up or down so that tibial acceleration may be measured in avertical direction at least. Data from sensors 10, 11 may be used toascertain medio-lateral deviation of the legs of subject 12 duringactivities and/or movements such as squatting, hopping and/or running.

Sensor data measured via sensors 10, 11 may be sent via wirelesstransmitters 13, 14 to remote receiver 15. Receiver 15 is associatedwith digital processing engine 16. Digital processing engine 16 includesa digital processor such as a microprocessor for processing data.

Digital processing engine 16 may include an algorithm for ascertainingmedio-lateral deviation of the knees using angular velocities andaccelerations measured from the antero medial aspect of each tibia.Digital processing engine 16 may perform calculations with the algorithmfollowing transformation of data from the frame of reference of eachsensor 10, 11 to the frame of reference of the mechanical axis of eachtibia.

In one form a digital memory or data storing means 17, 18, may beassociated with sensors 10, 11 for storing data in digital format foranalysis and/or reporting. Digital memory 17, 18 may include structuresuch as flash memory, memory card, memory stick or the like for storingdigital data. The memory structure may be removable to facilitatedownloading the data to a remote processing device such as a PC or otherdigital processing engine.

The digital memory 17, 18 may receive data from sensors 10, 11. Eachsensor 10, 11 may include or be associated with an analog to digital (Ato D) converter 19, 20. The or each A to D converter 19, 20 and memory17, 18 may be associated directly with sensors 10, 11 such as beinglocated on the same PCB as sensors 10, 11 respectively. Alternativelysensors 10, 11 may output analog data to transmitters 13, 14 and one ormore A to D converters may be associated with remote receiver 15 and/ordigital processing engine 16. The one or more A to D converters mayconvert the analog data to a digital domain prior to storing the data ina digital memory such as a digital memory described above. In someembodiments digital processing engine 16 may process data in real timeto provide biofeedback to subject 12 being monitored.

FIG. 2 shows a top-down cross-sectional view in the transversal plane ofthe left leg of subject 12 with sensor 10 placed on face 20 of tibia 21.The angle between face 20 on tibia 21 and the forward flexion plane isdefined as Φ. Angle Φ may be approximately 45 degrees for an averagesubject but may vary a few degrees up or down from the average value.Face 20 may provide a relatively stable platform for attachment ofsensor 10. The frame of reference (B) for sensor 10 is therefore rotatedrelative to the frame of reference (C) of the mechanical axis of tibia21 by the magnitude of angle Φ. Flexion and lateral flexion are definedas rotations around axes C_(Y) and C_(Z) while gyroscope andaccelerometer sensitivity axes of sensor 10 are aligned with axes B_(Y)and B_(Z).

Because measurements via sensor 10 are obtained in sensor referenceframe B they must be converted to tibia reference frame C. The followingequations may be used for this transformation:

Cy=By*cos(Φ)+Bz*sin(Φ)   (1)

Cz=By*sin(Φ)−Bz*cos(Φ)   (2)

wherein By, Bz denote y and z components in sensor reference frame B, Cyand Cz denote y and z components in tibia reference frame C, and Φdenotes the angle between sensor 10 on tibia 21 and the forward flexionplane.

Equations (1) and (2) above may be used to vector transform gyroscopesignals {^(B)ω_(x),^(B)ω_(Y) and ^(B)ω_(Z)} and optionally accelerometersignals {^(B)a_(x), ^(B)a_(Y) and ^(B)a_(Z)} obtained via sensor 10 insensor reference frame B, to gyroscope signals {^(C)ω_(x), ^(C)ω_(Y) and^(C)ω_(Z)} and accelerometer signals {^(C)a_(x), ^(C)a_(Y) and^(C)a_(Z)} respectively in mechanical or tibia reference frame C.

Following vector transformation, the gyroscope signals {C_(ω) _(x),^(C)ω_(Y) and ^(C)ω_(Z)} representing angular velocity may be integratedover a period of time t representing the duration of an activity such assquatting, hopping and/or running using the following equation toprovide an integrated angular displacement (θ):

θ=∫₀ ^(t)ω.dt   (3)

The integrated signals e may be corrected for gyroscope drift errorscaused by noise and/or other artefacts. Drift correction may beperformed using a known angular reference provided by the accelerometersignals. The flexion angle (θ_(Y)) may be corrected for drift at thestart and at the end of a hop/squat using the flexion angle (β_(y))obtained from the accelerometer signals using the following equation:

β_(y)=atan(^(c)a_(y)/^(c)a_(x))   (4)

The lateral flexion angle (θ_(Z)) may be corrected for drift usinglateral flexion angle (β_(z)) obtained from the accelerometer using thefollowing equation:

β_(z)=atan(^(c)a_(z)/^(c)a_(x))   (5)

The twist angle (θ_(X)) may be corrected with zero as there is norotation around gravity measured by the accelerometer.

As a player flexes the knee, the degree of medio/lateral deviation ismeasured with respect to mechanical or tibia reference frame (C).However, this value is transformed with respect to the visual referenceframe of the tester, also known as the frontal or viewer plane toprovide more intuitive results.

It is possible for the leg to rotate around the x-axis when the playerhops and lands. Hence, the visual impression of the lateral flexion willchange if the rotation around the x-axis is not compensated. This effectis represented in equation 7, as it is used in the projection of thelateral flexion plane (θ_(z)) with respect to the frontal plane.

FIG. 3 shows a projection of lateral flexion angle (θ_(Z)) onto thefrontal or viewer plane together with a twist update. To project lateralflexion angle (θ_(Z)) onto the frontal or viewer plane the leg mayconsidered to be a rigid rod with fixed joint on the ankle. The lengthof the rod may be normalized as 1. Angular displacement on the θ_(X)plane (caused by θ_(Y) and θ_(Z) only) may be determined by:

θ_(x0)=atan(sin(θ_(Z))/tan(θ_(Y)))   (6)

Actual twist movement θ_(x0) may be added to angular displacement θ_(X)to determine resultant angular displacement θ_(Xresultant):

θ_(xresultant)=θ_(x)+θ_(x0)  (7)

One goal is to determine the terms A, B and C in order to calculateθ_(zAdjusted). For this, the projection of θ_(Z) on θ_(X), will resultin A:

A=sin(θ_(Z))/sin(θ_(x) 0)*sin(θ_(x))   (8)

The projection of θ_(X) on θ_(Y) will determine B:

B=sin(θ_(Z))/sin(θ_(x0))*cos(θ_(x))   (9)

C is calculated assuming the length of the rod is 1:

C=sqrt(1−B²)   (10)

Finally, calculate asin of A and C to obtain the drift adjusted θ_(Z)and projected onto the frontal plane as θ_(zAdjusted):

θ_(ZAdjusted)=asin(A/C)   (11)

FIG. 4 shows test results for a subject with normal angular deviation ofthe knee during a jump. In FIG. 4, curve 40 represents flexion angle(θ_(Y)) in degrees plotted over the duration of the jump, while curve 41represents lateral flexion angle (θ_(Z)) in degrees plotted over thesame duration of the jump. Curve 41 shows reduced medio-lateraldeviation of flexion indicating negligible rotation around the y axis.Therefore the test indicates that this subject exhibits little or nomedio-lateral deviation i.e. neither valgus nor varus.

FIG. 5 shows test results for another subject with significant angulardeviation of the knee during a jump. In FIG. 5, curve 50 representsflexion angle (θ_(Y)) in degrees plotted over the duration of the jump,while curve 51 represents lateral flexion angle (θ_(Z)) in degreesplotted over the same duration of the jump. Curve 51 shows positivelateral deviation indicating approximately +18 degree rotation aroundthe y axis. Therefore the test indicates that this subject exhibitsVarus deviation i.e. the knee deviates outwards.

FIG. 6 shows test results for another subject with significant angulardeviation of the knee during a jump. In FIG. 6, curve 60 representsflexion angle (θ_(Y)) in degrees plotted over the duration of the jump,while curve 61 represents lateral flexion angle (θ_(Z)) in degreesplotted over the same duration of the jump.

Curve 61 shows negative lateral flexion angles indicating approximately−15 degree rotation around the y axis. Therefore the test indicates thatthis subject exhibits Valgus deviation i.e. the knee deviates inwards.

Finally, it is to be understood that various alterations, modificationsand/or additions may be introduced into the constructions andarrangements of parts previously described without departing from thespirit or ambit of the invention.

1. Apparatus for monitoring, measuring and/or estimating deviation of abody part of a vertebral mammal, said apparatus including: at least onesensor for measuring rotation of said body part relative to a firstframe of reference and for providing data indicative of said rotation; amemory device adapted for storing said data; and a processor adapted forprocessing said data to evaluate a deviation of said body part thatcorrelates to said data.
 2. Apparatus according to claim 1 wherein saidprocessor is configured to execute an algorithm for evaluating deviationof said body part.
 3. Apparatus according to claim 2 wherein saidalgorithm is adapted to transform said data from said first frame ofreference relative to a second frame of reference in which said bodypart performs a movement.
 4. Apparatus according to claim 1 wherein saidalgorithm is adapted to integrate said data over a period of time toprovide an angular displacement (θ).
 5. Apparatus according to claim 4wherein said algorithm is adapted to evaluate a component (θZ) of saidangular displacement representing valgus or varus angle.
 6. Apparatusaccording to claim 5 wherein said algorithm is adapted to project saidlateral flexion component (θZ) onto a frontal plane.
 7. Apparatusaccording to claim 4 wherein said algorithm is adapted to evaluate atwist component (θX) of said angular displacement representing twistangle.
 8. Apparatus according to claim 7 wherein said algorithm isadapted to compensate said twist component (θX) by adding an angularoffset (θx0) to said twistcomponent (θX).
 9. Apparatus according toclaim 8 wherein said angular offset (θx0) is caused by components θY andθz of said angular displacement and is determined byθx0=atan(sin(θZ)/tan(θY)).
 10. Apparatus according to claim 1 whereinsaid at least one sensor includes a gyroscope.
 11. Apparatus accordingto claim 1 wherein said at least one sensor is adapted for measuringrotation around one or more orthogonal axes.
 12. Apparatus according toclaim 1 wherein said at least one sensor further includes means formeasuring acceleration of said body part relative to an inertial frameof reference and for providing data indicative of said acceleration. 13.Apparatus according to claim 12 wherein said acceleration means isadapted for measuring acceleration along one or more orthogonal axes.14. Apparatus according to claim 1 wherein said body part of said mammalincludes legs and said apparatus is adapted to monitor rotationcomponents associated with said legs.
 15. Apparatus according to claim 1wherein respective sensors are applied to the legs of said mammal. 16.Apparatus according to claim 1 wherein the or each sensor includes ananalog to digital (A to D) converter for converting analog data to adigital domain.
 17. Apparatus according to claim 16 wherein said A to Dconverter is configured to convert an analog output from the or eachsensor to said data prior to storing said data.
 18. Apparatus accordingto claim 1 including means for providing feedback of said deviation to asubject being monitored.
 19. A method of monitoring, measuring and/orestimating deviation of a body part of a vertebral mammal, said methodincluding: using at least one sensor to measure rotation of said bodypart relative to a frame of reference and for providing data indicativeof said rotation; storing said data in a memory device; and processingsaid data by a processor to evaluate a deviation of said body part thatcorrelates to said data.
 20. A method according to claim 19 wherein saidprocessor is configured to execute an algorithm for evaluating deviationof said body part.
 21. A method according to claim 20 wherein saidalgorithm is adapted to transform said data from said first frame ofreference relative to a second frame of reference in which said bodypart performs a movement.
 22. A method according to claim 19 whereinsaid algorithm is adapted to integrate said data over a period of timeto provide an angular displacement (θ).
 23. A method according to claim22 wherein said algorithm is adapted to evaluate a component (θZ) ofsaid angular displacement representing valgus or varus angle.
 24. Amethod according to claim 23 wherein said algorithm is adapted toproject said lateral flexion component (θZ) onto a frontal plane.
 25. Amethod according to claim 22 wherein said algorithm is adapted toevaluate a twist component (θX) of said angular displacementrepresenting twist angle.
 26. A method according to claim 25 whereinsaid algorithm is adapted to compensate said twist component (θX) byadding an angular offset (θx0) to said twist component (θX).
 27. Amethod according to claim 26 wherein said angular offset (θx0) is causedby components θY and θz of said angular displacement and is determinedby θx0=atan(sin(θZ)/tan(θY)).
 28. A method according to claim 19 whereinsaid at least one sensor includes a gyroscope.
 29. A method according toclaim 19 wherein said at least one sensor is adapted for measuringrotation around one or more orthogonal axes.
 30. A method according toclaim 19 wherein said at least one sensor further includes means formeasuring acceleration of said body part relative to an inertial frameof reference and for providing data indicative of said acceleration. 31.A method according to claim 30 wherein said acceleration means isadapted for measuring acceleration along one or more orthogonal axes.32. A method according to claim 19 wherein said body part of said mammalincludes legs and said method includes monitoring rotation componentsassociated with said legs.
 33. A method according to claim 19 whereinrespective sensors are applied to the legs of said mammal.
 34. A methodaccording to claim 19 wherein the or each sensor includes an analog todigital (A to D) converter for converting analog data to a digitaldomain.
 35. A method according to claim 34 wherein said A to D converteris configured to convert an analog output from the or each sensor tosaid data prior to storing said data.
 36. A method according to claim 19including providing feedback of said deviation to a subject beingmonitored.